Bleached state transmittance in charge-unbalanced all-solid-state electrochromic devices

Abstract

The bleached state transmittance of a charge-unbalanced, complementary electrochromic (EC) device may show residual coloration due to the presence of residual charges. In this study, EC devices were fabricated with configurations G/ITO/Ni(OH)2/Ta2O5/H+–SPE/Ta2O5/WO3/ITO/G and G/ITO/NiOOH/Ta2O5/H+–SPE/Ta2O5/HWO3/ITO/G (G=glass, H+–SPE=proton-conducting solid polymer electrolytes, and ITO=indium tin oxide). These devices, referred to as EC1 and EC2, were initially fabricated from fully bleached EC layers and from fully colored EC layers, respectively. The change in electrochromic properties as a function of charge capacity ratio (R) for each device was then compared. In comparison to EC2 devices, EC1 devices provided better bleached-state transmittances and higher coloration efficiencies over a wider range of R, and were less sensitive to changes in R value. This may arise because the absorbance caused by the residual charges in the colored state is greater and more sensitive to the charge capacity ratio than that in the bleached state.